1. Field of the Invention
The present invention relates to a stamp device provided with a stamp plate constructed from a porous base plate wherein an ink impermeable melted-solidified portion and an ink permeable non-melted portion are formed by selectively heating and melting a stamp surface of the porous base plate having open cells through a thermal head having a plurality of dot heating elements, and a support member which supports the stamp plate from one side thereof, and more particularly to a stamp device with improved various stamping characteristics by giving various characteristics to the porous base plate used for the stamp plate.
The present invention also relates to a stamp plate producing apparatus for producing a stamp plate constructed from a porous base plate on which an ink permeable non-melted portion (figure portion) and an ink impermeable melted-solidified portion (non-figure portion) are formed by contacting a thermal head having a plurality of dot heating elements to a stamp surface of the porous base plate with ink permeability and selectively heating and melting the stamp surface of the porous base plate while moving the thermal head.
2. Description of Related Art
(1) Heretofore, a number of proposals have been made regarding stamp devices each using a stamp plate constructed from a porous base plate formed of cellular plastic or rubber having open cells therein, on which an ink permeable non-melted portion and an ink impermeable melted-solidified portion are formed by selectively heating and melting a stamp surface of the porous base plate by means of a thermal head. The ink permeable non-melted portion is the portion where open cells are left according to the shape of mirror images and the like to be stamped. The ink impermeable melted-solidified portion is the portion where open cells in the portion excepting the above part forming the mirror images are melted and solidified to be sealed.
When stamping of characters and the like is conducted by using the above stamp device, ink is impregnated in the non-melted portion of the stamp plate and the stamp plate is pressed onto a stamp sheet, thereby stamping of characters is done.
By the way, in the above stamp device, it is inevitable to be able to clearly stamp characters over plural stamping times, on the basis of characteristic in the stamp device. Therefore, it is demanded the following characteristics for the stamp device. That is, the first characteristic is that the non-melted portion in the stamp plate can satisfactorily retain ink therein. The second characteristic is that the border between the melted-solidified portion and the non-melted portion can be sharply formed by means of the thermal head. The third characteristic is that edges of characters can also be clearly stamped. And the fourth characteristic is that dimension of the stamp plate can be retained for a long time.
In order to satisfy the above characteristics, pore size (diameter) formed on the basis of open cells in the porous base plate used for the stamp plate, hardness of the stamp surface, melting point and thickness of the stamp plate, must be set in a suitable range. However, it is difficult to produce the stamp plate so as to satisfy the above characteristics demanded therefor, and sufficient study on the stamp plate has not been made yet.
(2) Conventionally, as shown in FIGS. 23, 24, it is well-known a stamp device 202. The stamp device 202 has a stamp plate 200 constructed from an ink permeable porous base plate on a surface of which stamping area is formed, and a support member 201 which supports the stamp plate 200 from the back surface thereof. The stamp device 200 can continuously stamp characters through the stamping area while impregnating ink in the stamp plate 200.
Further, it is well-known a stamp plate producing apparatus in which the stamp plate 200 used for the above stamp device 202 is produced. In such apparatus, the thermal head having dot heating elements is contacted to the surface of the ink permeable porous base plate and the dot heating elements are selectively heated while moving the thermal head. Thereby, it is formed on the surface of the porous base plate a stamp surface having the ink impermeable melted-solidified portion 203 (non-figure portion) and the ink permeable non-melted portion 204 (figure portion).
By the way, when the stamp surface is formed by selectively heating the dot heating elements while moving the thermal head on the surface of the porous base plate, the border between the melted-solidified portion 203 and the non-melted portion 204 is forcedly dragged by the edge of the thermal head in case that the dot heating elements are positioned upstream the moving direction of the thermal head from the contact point between the thermal head and the porous base plate. As a result, there is a problem that the border between the melted-solidified portion 203 and the non-melted portion 204 cannot be made clear. For example, as shown in FIG. 23, the central portion of the porous base plate (stamp plate 200) is dragged and extended in the direction E by the thermal head when melted, and after the stamp plate 200 is produced, the central portion of the porous base plate is contracted in the direction F as shown in FIG. 24. Thereby, torsion occurs in the stamp plate 200.
Reversely, if the dot heating elements are positioned downstream in the moving direction of the thermal head from the contact point between the thermal head and the porous base plate, the dot heating elements cannot be uniformly contacted to the porous base plate in case that the distance between the edge of the thermal head and the dot heating elements becomes long to an extent passing the limit.
(3) As mentioned, it is conventionally known a stamp plate producing apparatus for producing the stamp plate on which an ink permeable non-melted portion (figure portion) and an ink impermeable melted-solidified portion (non-figure portion) are formed by contacting a thermal head having a plurality of dot heating elements to a stamp surface of a porous base plate with ink permeability and selectively heating and melting the stamp surface of the porous base plate while moving the thermal head.
In the thermal head, the dimension of the dot heating element in both the primary scanning direction and the secondary scanning direction is generally set so as to become smaller than the dot pitch and the feed pitch, respectively, taking into consideration ink blurring in stamping.
However, in case that the stamp surface is formed on the porous base plate by selectively melting, it is necessary to be able to form the melted-solidified portion corresponding to one dot heating element by heating one element and to form the non-melted portion corresponding to one dot heating element without heating one element.
The inventors have variously studied to realize both melting one dot area corresponding the one dot heating element and remaining thereof without melting, as a result, found that it was important to consider the relation between the melting area and the energy applied to the thermal head. For example, as shown in FIG. 20, the melting area is apt to be influenced by change of the energy in the low energy region, thus stable melting cannot be done. On the other hand, it is possible that the thermal head is broken in the high energy region. Therefore, the energy for stable melting should be in a predetermined region.
Further, considering the melting area, to completely seal the melted-solidified portion it is necessary that the melting area has the same size of the dot pitch, as shown in FIG. 21(A) and (B). On the other hand, as shown in FIG. 22, since the non-melted portion is pressed while stamping, the non-melted portion can be wholly used as the stampable area, thus if the stampable area is about 70% of the dot pitch, stamping for the one dot area can be done taking ink blurring into consideration. At that time, the melting area necessary to remain the non-melted portion of the one dot area becomes about 110% of the dot pitch.
Assuming that the thermal head is driven with the energy region capable of melting the porous base plate, the inventors found that the melting area necessary to completely seal the melted-solidified portion and to remain the non-melted portion corresponding to the one dot area became 100%-110% of the dot pitch. Based on the above, this invention was made.